This invention relates to a heat-sensitive stencil, to a process of fabricating same and a method of producing a printing master using same.
One known heat-sensitive stencil is composed of an ink-permeable thin paper serving as an ink support and a thermoplastic resin film bonded with an adhesive to the support. The stencil is heated imagewise by, for example, a thermal head to perforate the heated portions of the thermoplastic resin film, thereby obtaining a printing master for reproducing images by mimeographic printing. An overcoat layer is generally provided over a surface of the thermoplastic resin film to prevent the sticking of the film with the thermal head.
The known heat-sensitive stencil has a problem, because the heated portions are not completely perforated. The portion of the stencil which remains unperforated results in a white spot in reproduced images obtained therefrom. This problem can be overcome by increasing thermal energy for the perforation. However, an increase of the thermal energy causes an increase of the master producing time as well as a shortened service life of the heating means.
A method has been proposed to increase the heat sensitivity of the stencil by reducing the thickness of the thermoplastic resin film, by using a low softening resin as the film or by using a resin having a great thermal shrinkage as the film. This method, however, requires an increased cost and, further, causes deterioration of physical properties of the stencil.
An attempt has also been made to increase the smoothness of the surface of the film with a view toward reducing perforation failure. JP-A-H5-212983 discloses a method of producing a smooth surface stencil by controlling a tension between a thermoplastic resin film and a support during lamination thereof. JP-A-H8-67081 discloses a method of producing a smooth surface stencil by heat-bonding a thermoplastic resin film and a support without using an adhesive. These methods give a smoothness of at most 5,000 seconds, even when the film originally has a surface smoothness of more than 10,000 seconds.